1. Field of the Invention
The present invention relates to a metallic bellows-type accumulator used in hydraulic piping of an automobile or the like as a pressure accumulation device or pulse pressure damping device or the like.
2. Description of the Conventional Art
The conventional metallic bellows-type accumulator 101 includes, as shown in FIG. 5(1), a shell 103 having an attachment portion 111 formed at one end to attach to a given system and having a gas plug 112 fixed at the other end to close a gas filling port for filling high pressure gas, and a metal bellows 107 capable of extending and contracting and disposed within the shell 103, one end of the metal bellows being fixedly secured to the shell 103 at the side of the attachment portion 111 and other end of the metal bellows being joined to a bellows cap 106, so that an inside of the shell 103 is partitioned into an outer gas chamber 104, in which high pressure gas is enclosed, at the side of the gas plug 112 and an inner liquid chamber 105, to and from which pressurized liquid is introduced and discharged. The metal bellows 107 has crest portions 107a at an outer diameter side and root portions 107b at an inner diameter side, each of the portions 107a and 107b having a sectional shape 107c in the axial direction in U-shape. The metal bellows 107 is configured such that, when contracted, a curvature radius Ra of U-shaped sections 107c of the crest portions 107a at the outer diameter side and a curvature radius Ra of the U-shaped sections 107c of the root portions 107b at the inner diameter side are reduced at the same rate. An oil port 108 is provided within the liquid chamber 105 for restricting the degree of contraction of the metal bellows 107, and a seal section 110 is attached to the bellows cap 106 at the side of attachment portion 111 for sealing a communication passage hole 109 provided on the upper wall 108a of the oil port 108 when the bellows cap 106 is brought into contact with the oil port 108.
With such structure, even in the case of system down and thereby the pressure in the liquid chamber 105 is reduced to cause larger contraction of the metal bellows 107, the further contraction of the metal bellows 107 is restricted by the bellows cap 106 which is in contact with the end surface of the upper wall 108a of the oil port 108. Furthermore, the seal section 110 attached to the bellows cap 106 seals the communication passage hole 109 formed on the upper wall of the oil port 108, thereby to prevent discharging of pressurized liquid from the liquid chamber 105 beyond a predetermined amount thereof. Therefore, abnormal deformation and resultant breakage of the metal bellows 107 are prevented (referring to Japanese unexamined patent publication No. 2003-343501 and Japanese unexamined patent publication No. 2004-108511).
However, in the above mentioned structure, when the metal bellows 107 is contracted to the extent of contacting with the oil port 108, the curvature radius Ra of the U-shaped sections 107c of the crest portion 107a at the outer diameter side and the curvature radius Ra of the U-shaped sections 107c of the root portion 107b at the inner diameter side are reduced at the same rate and become to be Rb, as shown in FIG. 5(2). Consequently, if a seal function of the seal section 110 becomes ineffective to cause pressurized liquid remaining in the liquid chamber 105 to be discharged, the pressure in the outer gas chamber 104 becomes higher than that of the inner liquid chamber 105, whereby abnormal deformation may occur at point or line contact portions 107d produced by the contraction of the crest portions 107a at the outer diameter side of the metal bellows 107 and the root portions 107b at the inner diameter side at the same rate, stress is thus concentrated to the contact portions 107d, and in the worst case, there may happen breakage of the metals bellows 107.